1. Field of the Invention
The present invention relates to a mold core used in an investment casting process and a process for preparing such a mold core, and further pertains to a process for preparing a mold for an investment molding process used with such a mold core.
2. Related Art Statement
A ceramic mold core used or assembled within a mold for an investment casting process should have a sufficiently smooth surface, a strength which is high enough to withstand the injection molding of a wax model and having a strength at high temperatures which is sufficient for retaining its integrity under high temperature environment, during the sintering and/or casting steps. Prior art cores conventionally used for such purposes are molded from aggregates, such as those containing alumina, zirconium or fused silica. Then the thus molded cores are burned or sintered singly. However, such a process leads to a low producibility or operation efficiency. In addition, it leads to the problem that the dimensional accuracy of the finished core is inferior, particularly in a preparation of a large size core, with extreme difficulty for obtaining a large-size core of accurate dimensions as well as an increase in production cost.
Further disadvantages of conventional sintered core molds are that they are hard to demolish after use. They cannot be removed from the casting by the application of physical vibrations or impact. Thus, cumbersome and inefficient operations are required for the removal of such cores.
In addition, in the production of such core molds which should be sintered for acquiring the necessary strength and integrity, some of the inexpensive aggregates, such as silinceous sand, cannot be used as the starting materials because of the difficulty encountered in sintering them.